The present invention relates to railcar truck assemblies and more specifically to an arrangement of the lands between the side frames and bolster of a railcar truck assembly. Particularly, at each intersection of the side frames with the bolster adjacent to the friction shoe wear plate interface, the facing lands are assembled at a gap separation distance of less than four-tenths inch. Assembly of the truck with this restriction provides an inhibition to truck warping with consequent improvement of truck hunting and curving performance during railcar operation.
In previous railcar truck assemblies, wide laterally extending stop surfaces or lands adjacent to the side frame wear plate and bolster friction shoe pocket have been provided to avoid rotation of the bolster about its longitudinal axis, that is bolster rotation. Further, each side frame of the railcar truck assembly has a longitudinal axis parallel to the truck longitudinal axis. The bolster longitudinal axis intersects and is perpendicular to the side frame longitudinal axes at an as-assembled condition. Rotation of the bolster about its central vertical axis causing angular displacement of the intersection of the side frame and bolster longitudinal axes from their perpendicular, as-assembled state is considered to be truck warping. These bolster positions presume an angled position relative to the side frames, as the bolster is generally perpendicular to the side frames at an as-assembled state. The angled positions for bolster rotation and warp were permitted by too great a clearance between the side frame column and the bolster. In the case of railcar truck warp, the greater clearance aggravates the conditions causing the wheel flanges to attack the rail at a relatively severe angle during curving, thus inducing excessive lateral forces. Further, if this column-bolster clearance is too great, truck assembly hunting may be aggravated.
Railcar truck hunting is a continuous instability of a railcar wheel-set where the truck weaves down the track in an oscillatory fashion, usually with the wheel flanges striking against the rail, creating wheel drag and increased lateral forces on the rail. A related condition referred to as lozenging is an unsquare condition of the side frames and bolster, and it occurs where sideframes operationally remain parallel to each other, but one sideframe moves slightly ahead of the other in a cyclic fashion; this condition is also referred to as parallelogramming or warping. Warping results in wheel misalignment with respect to the track; it is more pronounced on curved track and usually provides the opportunity for a large angle-of-attack to occur. The displacement or rotation of the bolster about the bolster vertical axis, which is accompanied by angling of its longitudinal axis relative to the side frame, is indicative of railcar truck warping. The concept of truck hunting, that is a highspeed dynamic instability of the railcar wheel sets is manifested by the parallelogramming or lozenging of the truck. Further, truck hunting is also a consequence of the lack of warp stiffness.
The above-noted wide stop surfaces were provided to inhibit rotation of the bolster in the side frame, which thus avoided the above-noted bolster rotational problems about its longitudinal axis; to permit as-cast surfaces to function properly; and, to avoid the wearing or eroding of the contacting surface edges between the bolster and the columns of the side frame bolster opening. In the illustration of U.S. Pat. No. 3,408,955 to Barber, the lands appear noticeably wider than the cited prior art lands. In practice, these wide lands have been noted as having a width of one and three-sixteenth inch (cf., Association of American Railroads, Mechanical Division, Manual of Standatds and Recommended Practices, D-II-200.25).
In a similar fashion, a bolster antirotation stop or lug was provided at the inside face of a side frame column to inhibit rotation of the bolster in the side frame, which also was to avoid the above-noted bolster rotational problems about its longitudinal axis. A representative structure of this stop lug arrangement is illustrated as Standard S-318-78 in the Manual of Standards and Recommended Practices of the Association of American Railroads, Mechanical Division at Page D-119.
The earlier practice of a narrow-land structure with a wide separation between the bolster land and side-frame, column-face land is illustrated in U.S. Pat. No. 2,378,415 to Light. In this patent, inboard and outboard column guide gibs are provided on the bolster for engagement with the inboard and outboard surfaces on the adjacent column. The outboard gibs in this structure have less depth than the widened portion of the bolster opening. A similar gib arrangement is taught in U.S. Pat. No. 2,422,201 to Lehrman. The significant separation distances between the side frame column and the bolster are clearly discernible in the plan views of the figures of these patents.
A technical study of a number of railcar derailments between 1988 and 1992 was conducted by a task force composed of representatives from five railroads, three railcar builders, three truck manufacturers, a major shipper, a major railcar fleet owner, as well as other component suppliers and technical consultants. The task force was to determine the cause of the derailments and to recommend both long-term and short-term solutions for derailment prevention. The results of the study are reported in Final Report, Testing, Evaluation & Recommendations Curving Performance of 125T DS Cars by Rail Sciences Inc. (RSI), Atlanta, Ga., Feb. 12, 1993. One of the parameters considered in the trucks was warp restraint, and as a consequence of the research it was determined that one of the five simultaneously occurring factors leading to the derailments being reviewed was `warping of sideframe-bolster due to low truck warp restraint`. One of the consequent longterm proposals resulting from the test determinations was to advocate the development and application of truck warp stiffening techniques. A principal finding of the study was that frame stiffening arrangements increase the warp restraint of the trucks and reduce lateral forces in curving. In addition, it was concluded that the studied derailments were the result of high lateral forces rolling the low rail or increasing total gage sufficient to allow a wheelset to drop in. One of the noted causes of these high lateral forces was warping of the sideframe-bolster combination due to low truck-warp restraint caused by the presence of resilient bearing adapter pads and a lack of friction wedge restraint. There were a plurality of other findings and conclusions from this study, which were noted in this report, however, the present invention only addresses the warping restraint within the railcar truck.